Detecting fetal growth restriction with customised assessment: Is the jury still out?
Authors: Kate Duhig, Jenny Myers
Journal: PLoS Medicine (2022)

Strategies to improve the detection of abnormal fetal growth trajectories in the antenatal period have received deserved attention, and much effort has focused on the development of fetal growth centile charts.In an accompanying research study in PLOS Medicine, Vieira and colleagues assess customised growth charts devised as part of the Growth Assessment Protocol (GAP) against standard care across 13 hospitals in England, in the DESiGN cluster randomised trial [1].Population-standard centiles charts are underpinned by the theory that fetal growth potential is comparable across populations and that aberrant growth may be attributed to environmental and nutritional factors.The alternative approach of fetal growth "customisation" argues that adjusting for maternal characteristics and parity can improve the precision of fetal growth restriction (FGR) detection, accounting for genetic factors that enthusiasts believe may significantly influence fetal growth [2].The GAP [3] was developed by the Perinatal Institute for the detection of small for gestational age (SGA) fetuses with customisation and includes a programme of risk assessment, training, and accreditation of the use of customised growth charts in antenatal care settings.The GAP programme customises fetal growth trajectories by adjusting for maternal height, weight, parity, and ethnicity.To date, there has been a lack of studies that prospectively compare the performance of population-based and customisationbased fetal growth assessment for either the detection of SGA or various other downstream adverse perinatal outcomes.The DESiGN trial had the aim of determining whether implementing GAP would improve antenatal detection of SGA.Thirteen hospital clusters in England were randomised to implementation of the GAP protocol or to standard care.Nearly 25,000 women were included in the analysis.The authors found no difference in the detection of SGA with GAP compared to standard practice.An observed reduction seen in the stillbirth rate in women exposed to the GAP intervention was 1 of 26 tested secondary outcomes with no statistical correction for multiplicity.Given that the detection of SGA was not improved with GAP (the intended mechanism of adverse outcome reduction), it seems possible that this is a type I error rather than a true effect.The pragmatism of the trial methodology made it a feasible endeavour, but standard care was hard to define, impossible to protocolise, and difficult data to capture.Importantly, scan frequency increased in both arms of the trial, and it was clearly unintentional that the largest increase in scan frequency was seen with standard care.In addition, there was poor fidelity with adherence to the GAP protocol: Only 8.5% of women with risk factors for SGA had at least the AU : Anabbreviationlisthasbeencompiledforthoseusedthroughoutthetext:Pleaseverifythatallentr minimum number of scans recommended by GAP.External factors beyond the control of the trial team included the national rollout of the "Saving Babies Lives (SBL) Care Bundle" implemented by NHS England [4].Explicit aims of SBL were to improve the detection of FGR and to reduce perinatal mortality.While the standard care clusters in the DESiGN trial